I haave two questions regards to LM7805.
My circuit draws approximately 200mA with peaks around 250mA. My LM7805 without heatsink becames wery hot. So hot that i burn my fingers when i touch it. Is that normal? It's a 5v circuit.
Is there any alternative to LM7805 that can takes more current and stay cooler?
Can this work as an replacement?
You haven’t said what the input voltage is to the LM7805, but assuming it is 12 volts and you are drawing 0.25 amps, then it will get hot. It has to burn off 1.75 watts.
Yes, a buck converter as illustrated is much more efficient.
"My LM7805 without heatsink becames wery hot. So hot that i burn my fingers when i touch it. Is that normal? It's a 5v circuit."
They get hot when under load, but check your wiring. If it is miss wired, it will get very hot very quickly, hot enough that you will start to smell it. You might get a UBEC 5/6v regulator off of ebay.
6v6gt:
You haven’t said what the input voltage is to the LM7805, but assuming it is 12 volts and you are drawing 0.25 amps, then it will get hot. It has to burn off 1.75 watts.
Yes, a buck converter as illustrated is much more efficient.
Input power is 9v.
After 30 minutes its wery hot, and i'm affraid the LM7805 can make my sircuit unstable over time. I therefore want to change it with a baetter solution.
Then i'm going to order the Buck converter i linked to over 
Did you put capacitors on the input and output of the LM7805?
If not it could be oscillating which would make it hot.
Grumpy_Mike:
Did you put capacitors on the input and output of the LM7805?
If not it could be oscillating which would make it hot.
Yes. i put two 47uF capacitors. one to 9v input and one for the 5v output.
I can messure the heat later to day and check back
Thanks, just checking as it is a common mistake not to use any.
That should have worked although in addition a 0.1uF ceramic is also recommended in parallel with them to take out high frequencies.
I would go ahead with the buck converter, make sure you have capacitors on the input and output of that as well.
Yes that buck converter is better. For more $ you can get adjustable output converters.
With a buck converter, it typically takes about 400mA 12V input to make 1A 5V output.
With a 7805 the input current is the same as the output current. Charge at 12V is dropped to 5V... potential energy (voltage) ties to mass (charge) turns into kinetic energy (heat). And you lose over half of the input unless you wanted a heater.
GoForSmoke:
Yes that buck converter is better. For more $ you can get adjustable output converters.With a buck converter, it typically takes about 400mA 12V input to make 1A 5V output.
With a 7805 the input current is the same as the output current. Charge at 12V is dropped to 5V... potential energy (voltage) ties to mass (charge) turns into kinetic energy (heat). And you lose over half of the input unless you wanted a heater.
isn't that buck converter i ordered (see link over) adjustable?
It is an turning wheel on it?
Bjerknez:
So hot that I burn my fingers when i touch it. Is that normal? It's a 5v circuit.
You've had good answers to everything else but, unless I missed it, no one addressed this. If it burns your fingers it's too hot. While semiconductors can withstand temperatures that are too hot to touch such temperatures should be avoided. Rule of thumb is to keep temperatures within what you can comfortably keep your finger (or thumb) on.
Simple answer, use a small heatsink. The 7805v is a nice quiet regulator being linear. These "fashionable" 'buck' converters introduce switching noise. May not be an issue to most projects, but worth bearing in mind.
That should have worked although in addition a 0.1uF ceramic is also recommended in parallel with them to take out high frequencies.
Do you mean two 0.1uF after the two 47uF?
Can you explain how to place theese?
What is you application? Linear regulators are often necessary for sensitive analog circuitry which can't afford switching noise, otherwise the increased efficiency of a SMPS is advantageous. Nothing fashionable about advantageous, just sound judgement.
Bjerknez:
Do you mean two 0.1uF after the two 47uF?Can you explain how to place these?
I don't know what you mean by 'after'. The capacitors should be placed as close to the pins of the regulator as physically possible, so maybe not more than 5mm or so away, closer if you can. The 0μ1 and 47μ0 would be right next to each other, there is no 'before' or 'after'.
PerryBebbington:
I don't know what you mean by 'after'. The capacitors should be placed as close to the pins of the regulator as physically possible, so maybe not more than 5mm or so away, closer if you can. The 0μ1 and 47μ0 would be right next to each other, there is no 'before' or 'after'.
So two 0.1uF ceramic capacitors after booth my other to 47uF capacitors?
Bjerknez:
So two 0.1uF ceramic capacitors after both my other to 47uF capacitors?
Sorry but I am struggling to know what you are not getting. On the input to the regulator a 0μ1 and 47μ0 capacitor between the input and the ground pin in parallel. On the output the same; a 0μ1 and 47μ0 capacitor between the output and the ground pin in parallel.
If that doesn't make sense then I don't know how else to explain it. There is no 'before' or 'after'.
Ok, thanks.
This is a LM7805 Data Sheet you may want to note the 0.1 uF cap on the output. They also use a 0.33 uF capacitor on the input. Those caps should be, as was mentioned, as close to the In/Out pins as possible. Next if the LM7805 is in a common TO220 case they make dozens of simple heat sinks for them including simple slip on designs. Easy to obtain and easy to use.
Ron
Bjerknez:
isn't that buck converter i ordered (see link over) adjustable?
It is an turning wheel on it?
yes it is, here's the whole spiel:
Mini DC-DC 12-24V To 5V 3A Step Down Power Supply Module Voltage Buck Converter Adjustable 97.5% 1.8V 2.5V 3.3V 5V 9V 12V
I stopped at the 12-24V To 5V 3A Step Down Power Supply Module when the whole line edits itself by the end. Whoever wrote that, it's just a bit lightly tossed word salad.
I have fixed-5V-output boost converters and some 3.3V-output 1A max rated buck converters that are the size, shape and pinout of 7803's just for making 3.3V device power.
they make dozens of simple heat sinks for them
I remember when screwing the tab onto chassis metal was enough!
But then the PS could work as a doorstop or boat anchor as well.
"I remember when screwing the tab onto chassis metal was enough!
But then the PS could work as a doorstop or boat anchor as well".
Dat true. Today there are so many things to make the life of an electronic enthusiast easier. Buck/Boost converters in small modular packages and a host of other really neat stuff off the boat for literally a few bucks (USD).
Ron